Flowing cryogenic liquid target for terahertz wave generation

Terahertz wave emission from liquids excited by intense laser pulses not only reflects the details in laser–matter interaction but also offers bright terahertz wave sources. Flowing liquid targets possess the advantage of providing a fresh area for each laser pulse. To demonstrate a debris-free target under laser excitation, we investigate the use of liquid nitrogen as a target. By creating a flowing liquid nitrogen line in an ambient environment, we successfully observe broadband terahertz wave emission under short pulse excitation. Our cryogenic line is able to sustain the excitation of a high-repetition-rate (1 kHz) laser. The terahertz peak field emitted from liquid nitrogen is comparable to that from liquid water, yet a broader bandwidth is observed. This demonstration prompts opportunities in choosing potential materials for studying terahertz wave generation processes and in understanding laser-induced ionization of different liquids.